The network virtualization technology in which more than one logical network is formed on a physical network is currently in practical use. For example, the tagged VLAN (virtual local area network) is a network virtualization technology. In the tagged VLAN, a tag including a VLAN identifier (VLAN-ID) is inserted in each frame. The communication devices which transfer frames (e.g., layer-2 switches) refer to tags, and control the forwarding directions of the respective frames so as to prevent mixing of a frame from a different VLAN. The tagged VLAN is used, for example, in a layer-2 network formed in a data center for separating frames on a user-by-user basis.
In a first conventionally proposed storage system, operations are load balanced between multiple storages, and a virtual storage system is established. (See, for example, International Patent Publication No. WO2006/055765.)
In a second conventionally proposed system, in order to reduce load concentration, information indicating the status of use of application software is provided to clients, and the clients access an application delivery server on the basis of the information indicating the status of use. (See, for example, Japanese Laid-open Patent Publication No. 2009-277089.)
In a conventionally proposed authentication method executed in a system in which terminals can receive services provided by a server without awareness of the location of the server, authentication of each terminal is enabled by attaching an electronic signature to each service request transmitted from the terminal. (See, for example, Japanese Laid-open Patent Publication No. 2010-191801.)
In a third conventionally proposed system, a repeater device which receives a message originated from a client and addressed to a server brings a tenant ID indicating a tenant to which the client belongs into correspondence with a connection ID. (See, for example, Japanese Laid-open Patent Publication No. 2010-219845.)
Incidentally, in some cases where a virtual network is formed by inserting a tag into a frame, there is an upper limit to the number of virtual networks which can be supported by a communication device, since the value which can be indicated by a tag is limited. For example, the VLAN-ID in the tagged VLAN is represented by 12 bits, and only 4094 VLAN-IDs, other than the two reserved VLAN-IDs, are available. Therefore, the maximum number of VLANs which can be supported by a layer-2 switch is 4094.
On the other hand, in some cases, formation of virtual networks in a number greater than the maximum number of VLANs which can be supported by a layer-2 switch is demanded. For example, formation of more than 4094 virtual networks on a layer-2 network is demanded in a data center.
In order to overcome the above problem, it is possible to consider a method of forming different virtual networks using identical tag information in different locations remote from each other in a physical network by arranging information processing devices performing communication by use of the identical tag information in such a manner that the range in which frames in each virtual network are transmitted is localized. However, according to this method, when the transmission paths are changed by redundancy control in case of failure, frames from different virtual networks using the identical tag information can flow into a communication device, so that collision of tag information can occur.